diff --git a/apps/drivers/drv_pwm_output.h b/apps/drivers/drv_pwm_output.h
index fe08d3fe57..23883323e2 100644
--- a/apps/drivers/drv_pwm_output.h
+++ b/apps/drivers/drv_pwm_output.h
@@ -103,6 +103,9 @@ ORB_DECLARE(output_pwm);
 /** set update rate in Hz */
 #define PWM_SERVO_SET_UPDATE_RATE	_IOC(_PWM_SERVO_BASE, 2)
 
+/** get the number of servos in *(unsigned *)arg */
+#define PWM_SERVO_GET_COUNT	_IOC(_PWM_SERVO_BASE, 3)
+
 /** set a single servo to a specific value */
 #define PWM_SERVO_SET(_servo)	_IOC(_PWM_SERVO_BASE, 0x20 + _servo)
 
diff --git a/apps/drivers/px4io/px4io.cpp b/apps/drivers/px4io/px4io.cpp
index 1678ed0de2..61c9a793d9 100644
--- a/apps/drivers/px4io/px4io.cpp
+++ b/apps/drivers/px4io/px4io.cpp
@@ -974,6 +974,10 @@ PX4IO::ioctl(file *filep, int cmd, unsigned long arg)
 		}
 		break;
 
+	case PWM_SERVO_GET_COUNT:
+		*(unsigned *)arg = _max_actuators;
+		break;
+
 	case PWM_SERVO_SET(0) ... PWM_SERVO_SET(PWM_OUTPUT_MAX_CHANNELS): {
 
 		unsigned channel = cmd - PWM_SERVO_SET(0);